Clean up and modernize parameters directory

[pnorton-usgs]

Clean up and modernize parameters directory

Summary

Removes dead code, modernizes type hints, replaces implicit __getattr__ delegation, fixes a fragile private method access pattern, and improves encapsulation across the parameters directory.

Changes

Dead code removal

• Delete ParameterSet.py — entire file was commented-out dead code (96 lines)
• Remove commented-out reshape method from Parameter.py (~45 lines)
• Remove commented-out size property, old namedtuple comments, debug prints
• Remove commented-out code from Parameters.py and ParameterFile.py

Modernize type hints

• Add from __future__ import annotations to all parameter files
• Replace typing.Dict, List, Set, Optional, Union with built-in generics and X | Y syntax
• Simplify super() calls to Python 3 style
• Fix verbose parameter types: Optional[bool] → bool (None was never meaningful)

Replace __getattr__ in Parameters

• Remove __getattr__ delegation to internal __parameters dict
• Add __contains__, __iter__, __len__ for Pythonic collection behavior
• Update exists() to use __contains__
• Improves IDE support, prevents accidental dict mutation

Fix fragile private method access

• Rename MetaData.__parameters_to_dict to MetaData._parameters_to_dict (single underscore)
• Update ParamDb.py to use the clean internal method name instead of name-mangled _MetaData__parameters_to_dict

Parameter.py minor improvements

• Add __repr__ method for debugging
• Add -> bool return type annotation to is_scalar property
• Replace isinstance(indices, type(dict().values())) with isinstance(indices, ValuesView) from collections.abc

Encapsulation

• parameters property now returns a MappingProxyType (read-only view) instead of the raw internal dict
• Prevents external code from bypassing add()/remove() by directly mutating the dict

Testing

All 290 tests pass.